Three streams are mixing at a junction. The flow rate and total dissolved solids (TDS, a conservative pollutant) for each is presented in the table below. An industry is discharging 800 cfs downstream of the junction. If the TDS concentration in the stream cannot exceed 250 mg/L, calculate the maximum concentration (in mg/L TDS) allowable in the industry effluent if steadystate conditions apply. Stream    Flow (cfs)     TDS (mg/L) 1                500                  60 2                700                  50 3              1,000                 75

10. A 15,000 ft³ conventional activated sludge system has a recycle ratio of 0.38, an influent flow rate of 17,000 ft°/day, a mixed liquor volatile suspended solids (MLVSS) concentration of 280 mg/L, and an influent BOD, of 60 mg/L. What is most nearly the recycle rate of the system? (A) 2800 ft/day (B) 3600 ft/day (C) 5300 ft/day (D) 6500 ft°/day А. В. O000

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Drainage from a former pesticide manufacturing site enters Bear River at river kilometer 240. The drainage contains DDT, and the concentration of DDT after complete mixing is 5 µg/L. The town of Bear Valley, adult population 15,000, uses the river at river kilometer 40 for its water supply with only chlorination. The drainage has occurred for 30 years. The river velocity is 5 cm/s. Assume the half-life of DDT is 70 days (a) The concentration of DDT in the town's drinking water is mostly nearly (A) 1.2 µg/L (B) 2.3 µg/L (C) 3.2 µg/L (D) 3.9 μg/L (b) With 2 L/day water consumption, adult body mass of 70 kg, and life expectancy of 70 years, the lifetime chronic daily intake of DDT for an adult living in Bear Valley is most nearly (A) 4 x 10³ mg/kg-day (B) 8 x 10 mg/kg-day (C) 6 x 10³ mg/kg-day (D) 2 x 10² mg/kg-day (c) Assume a slope factor of 0.34 (mg/kg-day)-¹ for DDT. The number of excess lifetime cancers that can be expected in the adult population of Bear Valley is most nearly (A)…